function animate(obj, target, callback) {
  clearInterval(obj.timer);
  obj.timer = setInterval(() => {
    var step = (target - obj.offsetLeft) / 10;
    step = step > 0 ? Math.ceil(step): Math.floor(step);
    obj.style.left = obj.offsetLeft + step + 'px';
    if(obj.offsetLeft == target){
      clearInterval(obj.timer);
      callback && callback();
    }
  }, 15);
}